The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of a rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air bearing surface (ABS) of the write head and the pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic flux in the pole pieces which causes a magnetic field to fringe out at a write gap at the ABS for the purpose of writing the aforementioned magnetic impressions in tracks on the moving media, such as in circular tracks on the aforementioned rotating disk.
In recent read head designs a spin valve sensor, also referred to as a giant magnetoresistive (GMR) sensor, has been employed for sensing magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, hereinafter referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, hereinafter referred to as a pinned layer and a free layer. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. The magnetization of the pinned layer is pinned perpendicular to the air bearing surface (ABS) and the magnetic moment of the free layer is located parallel to the ABS, but free to rotate in response to external magnetic fields. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer.
The thickness of the spacer layer is chosen to be less than the mean free path of conduction electrons through the sensor. With this arrangement, a portion of the conduction electrons is scattered by the interfaces of the spacer layer with each of the pinned and free layers. When the magnetizations of the pinned and free layers are parallel with respect to one another, scattering is minimal and when the magnetizations of the pinned and free layer are antiparallel, scattering is maximized. Changes in scattering alter the resistance of the spin valve sensor in proportion to cos θ, where θ is the angle between the magnetizations of the pinned and free layers. In a read mode the resistance of the spin valve sensor changes proportionally to the magnitudes of the magnetic fields from the rotating disk. When a sense current is conducted through the spin valve sensor, resistance changes cause potential changes that are detected and processed as playback signals.
A spin valve sensor is characterized by a magnetiresistive (MR) coefficient that is substantially higher than the MR coefficient of an anisotropic magnetoresistive (AMR) sensor. For this reason a spin valve sensor is sometimes referred to as a giant magnetoresistive (GMR) sensor. When a spin valve sensor employs a single pinned layer it is referred to as a simple spin valve. When a spin valve employs an antiparallel (AP) pinned layer it is referred to as an AP pinned spin valve. An AP spin valve includes first and second magnetic layers separated by a thin non-magnetic coupling layer such as Ru. The thickness of the spacer layer is chosen so as to antiparallel couple the magnetizations of the ferromagnetic layers of the pinned layer. A spin valve is also known as a top or bottom spin valve depending upon whether the pinning layer is at the top (formed after the free layer) or at the bottom (before the free layer). A pinning layer in a bottom spin valve is typically made of platinum manganese (PtMn). The spin valve sensor is located between first and second nonmagnetic electrically insulating read gap layers and the first and second read gap layers are located between ferromagnetic first and second shield layers. In a merged magnetic head a single ferromagnetic layer functions as the second shield layer of the read head and as the first pole piece layer of the write head. In a piggyback head the second shield layer and the first pole piece layer are separate layers.
Sensors can also be categorized as current in plane (CIP) sensors or as current perpendicular to plane (CPP) sensors. In a CIP sensor, current flows from one side of the sensor to the other side parallel to the planes of the materials making up the sensor. Conversely, in a CPP sensor the sense current flows from the top of the sensor to the bottom of the sensor perpendicular to the plane of the layers of material making up the sensor.
Yet another type of sensor, somewhat similar to a CPP GMR sensor is a Tunnel Valve. A tunnel valve employs an electrically insulating spacer layer rather than a conductive spacer layer. A tunnel valve operates based on quantum mechanical tunneling of electrons through the insulating spacer layer. This tunneling is maximized when the magnetizations of the free and pinned layers are parallel to one another adjacent to the spacer layer.
The extremely competitive data storage market requires ever increasing data density and data rate capabilities from memory devices such as disk drives. This need for increased data storage capabilities has lead to increased interest in perpendicular recording. In a perpendicular recording system, data is recorded by magnetic fields directed perpendicular to the surface of the magnetic medium. Researchers have found that CPP GMR sensors are especially suited for use in such perpendicular magnetic recording. There is therefore, an increased need for a practical CPP sensor that can be used in such a perpendicular recording systems.
The demand for increased data density has also lead to an ever increasing need for smaller track width sensors. By making the track width of a sensor smaller, a greater number of tracks of data can fit onto a given disk. Current manufacturing techniques are fast approaching the limit to which the track width of a sensor can be shrunk, such as for example, photolithographic processes used to pattern a mask to form sensor.
Traditionally, sensors have been constructed, by depositing a full film of sensor material, on a substrate. A photoresist mask is then formed over an area that is to be the sensor and other areas are left uncovered. The photoresist mask has been constructed by spinning on a layer of photoresist and then photolithographically developing the photoresist to form the mask. Factors such as the wavelength of light used to develop the photoresist, effects of photoresist thickness on focal length, and material properties of the photoresist, limit the amount by which the track width of a sensor can be reduced.
After the photoresist mask has been defined, an ion mill is used to remove unwanted sensor material in the unmasked regions. This ion milling process deleteriously affects a portion of the sensor at the sensor edges. Ion bombardment of the sensor material at the sides of the sensor damages the sensor material at the sides leaving a percentage of the side portions of the sensor infective for sensing magnetic signals. With a great enough sensor width, the amount of damaged sensor material makes up only a small percentage of the total sensor material and the effect is negligible. However, as sensor widths (ie. track widths) decrease, the percentage of damaged sensor material increases to the point where sensor performance is seriously degraded.
Another problem associated with the ion milling process described above is that the use of ion milling requires the use of a thicker photoresist mask than would otherwise be necessary. As those skilled in the art will appreciate, increased photoresist thickness undesirably affects focus depth during the photolithography process, leading to poorer patterning resolution.
Therefore, there is a strong felt need for methods manufacturing high performance sensor having very small track widths. There is also a strong felt need for a method of constructing such a small trackwidth sensor as a CPP sensor.